A variety of production fluids are pumped from subterranean environments. Different types of submergible pumping systems may be disposed in production fluid deposits at subterranean locations to pump the desired fluids to the surface of the earth.
For example, in producing petroleum and other useful fluids from production wells, it is generally known to provide a submergible pumping system for raising the fluids collected in a well. Production fluids, e.g. petroleum, enter a wellbore drilled adjacent a production formation. Fluids contained in the formation collect in the wellbore and are raised by the submergible pumping system to a collection point at or above the surface of the earth.
A typical submergible pumping system includes several components, such as a submergible electric motor that supplies energy to a submergible pump. The system further may include a variety of additional components, including a connector used to connect the submergible pumping system to a deployment system. Conventional deployment systems include production tubing, cable and coiled tubing. Additionally, power is supplied to the submergible electric motor via a power cable that runs along the deployment system.
Often, the subterranean environment, and specifically the well fluid, contains corrosive compounds that may include CO.sub.2, H.sub.2 S and brine water. These corrosive agents can be detrimental to components of the submergible pumping system, particularly to internal electric motor components, such as copper windings and bronze bearings.
Submergible electric motors are difficult to protect from corrosive agents because of their design requirements that allow use in the subterranean environment. A typical submergible motor is internally filled with a fluid, such as a dielectric oil, that facilitates cooling and lubrication of the motor during operation. As the motor operates, however, heat is generated, which, in turn, heats the internal motor oil causing expansion of the oil. Conversely, the motor cools and the motor oil contracts when the submergible pumping system is not being used.
Accordingly, this type of submergible motor requires a motor oil expansion system able to accommodate the expanding and contracting motor oil. Also, the internal pressure of the motor must be allowed to equalize or at least substantially equalize with the surrounding pressure found within the wellbore. As a result, it becomes difficult to prevent the ingress of corrosive agents into the motor oil and internal motor components.
Numerous types of motor protectors have been designed and used in isolating submergible motors while permitting expansion and contraction of the internal motor oil. A variety of elastomeric bladders alone or in combination with labyrinth sections have been used as a barrier between the well fluid and the motor fluid. For example, expandable elastomeric bags or bladders have been used in series to prevent mixing of wellbore fluid with motor oil while permitting expansion and contraction of the motor oil.
In this latter design, the motor protector includes a pair of chambers that each have an elastomeric bladder. The first bladder is disposed in a first chamber of the pair of chambers and includes an interior in fluid communication with the motor. This fluid communication permits motor oil to flow from the motor into the elastomeric bladder during expansion and to flow from the elastomeric bladder back to the motor during contraction.
The second chamber also includes an expandable bladder, filled with motor oil, that is in fluid communication with the first chamber but external to the first elastomeric bladder. The second chamber also is vented or open to the wellbore environment. This permits fluid to flow between the second elastomeric bladder and the adjacent chamber as the first elastomeric bladder expands or contracts. Simultaneously, wellbore fluid is allowed to flow in and out of the second chamber, external to the second elastomeric bladder, to permit equalization of pressure as the second bladder expands and contracts.
This type of expansion chamber works well in many environments, but certain of the corrosive agents found in at least some wellbore environments include corrosive gases that permeate the elastomeric bags or bladders. These corrosive agents eventually can work their way into the motor oil within the first elastomeric bladder and ultimately corrode and damage internal components of the electric motor.
It would be advantageous to utilize an expandable bladder system in a motor protector without the threat of corrosive agents migrating to the internal components of the electric motor.